The present invention relates to handling of semiconductor wafers and other articles.
In a typical integrated circuit manufacturing process, semiconductor wafers are handled by a computer controlled robot. The robot is required to position the wafers with much precision to avoid wafer damage or misalignment between different processing stages. A wafer can be damaged, for example, if it is unintentionally rubbed against a wall of a storage container into which the wafer is being lowered by the robot.
Absolute precision is impossible to achieve. Usually there are some errors in the wafer""s position relative to the robot and the robot""s position relative to a target station into which the wafer is placed by the robot.
Some embodiments of the present invention allow one to reduce or eliminate the impact of wafer positioning errors. In some embodiments, the robot""s wafer holder (xe2x80x9cend effectorxe2x80x9d) is constructed to allow the wafer to slide relative to the holder without the holder losing control of the wafer. For example, the holder may have protrusions on its surface. The robot generates a force that draws the wafer to the holder so that the wafer is pressed against the protrusions. The friction force between the wafer and the protrusions prevents the wafer from moving relative to the holder when the robot is transporting the wafer between stations, but allows the wafer to slide on the protrusions when the robot pushes the wafer against a pin or pins precisely positioned relative to a target station. The pin or pins steer the wafer into a precise position relative to the target station even though the holder position relative to the target station may be imprecise. The robot then places the wafer into the target station.
The invention is not limited to the embodiments described above, but is defined by the appended claims.